Move examples/*.sx and their expected/ snapshots into per-category
subfolders (examples/<category>/...). Folder = leading filename token,
with ffi-objc/ffi-jni kept whole; filenames are unchanged. The corpus
runner and LSP sweep now discover each category's expected/ dir, while
issues/ stays flat. Example 1058's repo-root-relative companion import
is made file-relative. Path strings embedded in 164 snapshots were
regenerated (path-only changes). Test-layout docs in CLAUDE.md updated.
Adds examples/1650-platform-asm-rw-place.sx exercising a `+r -> @x`
read-write place output. Currently rejected loudly at lowering
("not yet implemented"); this locks that behavior as a passing test.
The next commit implements read-write outputs and flips this example
to run end-to-end (increment-in-place → 42).
